Process for preparing 4-cyclohexyl-2-methyl-2-butanol

ABSTRACT

A process for preparing 4-cyclohexyl-2-methyl-2-butanol, comprising:
         a) reaction of styrene with isopropanol at elevated temperature to obtain 2-methyl-4-phenyl-2-butanol, and   b) heterogeneously catalyzed hydrogenation of 2-methyl-4-phenyl-2-butanol over a catalyst suitable for ring hydrogenation of aromatics,
 
where the molar ratio of the styrene used in step a) to the isopropanol used in step a) is in the range from 1:below 5 to 1:0.5.

CROSS-REFERNCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent App. Ser. No. 61/535,381, filed Sep. 16,2011, whichis incorporated herein by reference in its entirety.

The present invention relates to a process for preparing4-cyclohexyl-2-methyl-2-butanol.

4-Cyclohexyl-2-methyl-2-butanol, which is also known as coranol, is afragrance with a lily-of-the-valley odor, the use of which as aconstituent of fragrance compositions was described for the first timein U.S. Pat. No. 4,701,278.

The preparation of 4-cyclohexyl-2-methyl-2-butanol was described by N.E. Okazawa et al. in Can. J. Chem. 60 (1982), 2180-93 and comprises theconversion of 3-cyclohexylpropanoic acid to the acid chloride, which isthen reacted with 2 mol of methyllithium to give4-cyclohexyl-2-methyl-2-butanol. Owing to the use of methyllithium, thispreparation process, especially in the case of performance on a largerscale, is afflicted with not inconsiderable risks and is economicallyunattractive. Nevertheless, no further preparation processes have beendescribed to date in the literature.

Unpublished application PCT/EP2011/054559 to the applicant describes aprocess for preparing 4-cyclohexyl-2-methyl-2-butanol. The processdescribed therein discloses the reaction of styrene with isopropanol atelevated temperature. Examples 1 to 4 disclose a reaction of styrenewith isopropanol, wherein the isopropanol is added batchwise to thereaction. The conversion in examples 1 to 4 is always more than 85%, andso the molar ratios of styrene to isopropanol in examples 1 to 4 arealways well above 1:5.

It is therefore an object of the present invention to provide aneconomically viable process for preparing4-cyclohexyl-2-methyl-2-butanol. This object is achieved by the processdescribed hereinafter, which comprises the following steps:

-   -   a) reaction of styrene with isopropanol at elevated temperature        to obtain 2-methyl-4-phenyl-2-butanol, and    -   b) heterogeneously catalyzed hydrogenation of        2-methyl-4-phenyl-2-butanol over a catalyst suitable for ring        hydrogenation of aromatics,

where the molar ratio of the styrene used in step a) to the isopropanolused in step a) is in the range from 1:below 5 to 1:0.5.

The process can be represented by the following reaction scheme:

The invention thus relates to a process for preparing4-cyclohexyl-2-methyl-2-butanol with the steps described here andhereinafter and in the claims.

The process is associated with a series of advantages. It allows thepreparation of 4-cyclohexyl-2-methyl-2-butanol from very inexpensivecommodity chemicals. The use of expensive and hazardous reagents such asmethyllithium is not required. Both step a) and step b) can be performedwithout any problem on the industrial scale, and afford the particularproducts with high selectivity and good yields.

In step a) of the process according to the invention, isopropanol isreacted with styrene at elevated temperature. This forms2-methyl-4-phenyl-2-butanol in the manner of a hydroxyalkylation, andby-products including toluene and ethylbenzene, which can, however, beremoved from the target product, for example, by distillation.

In the context of an analytical study of the reaction of styrene withalkanols under supercritical conditions, the reaction was reported by T.Nakagawa et al. (see J. Supercritical Fluids, 27 (2003), p. 255-261 andTetrahedron Left, 48 (2007), p. 8460-8463). However, the reaction wasnot utilized to preparatively obtain 2-methyl-4-phenyl-2-butanol.

With regard to the selectivity of the reaction, it has been found to beadvantageous when reaction in step a) is performed under supercriticalconditions. This is understood to mean reaction conditions under whichat least one of the components of the reaction mixture, preferably theisopropanol, is in the supercritical state. Accordingly, in a preferredembodiment of the process according to the invention, the reaction instep a) is effected under conditions under which isopropanol is in thesupercritical state. The critical temperature T_(c) of isopropanol is235° C.; the critical pressure P_(c) is 4.8 MPa. Supercriticalconditions can be established by the person skilled in the art byvarying pressure and temperature.

The temperature required for a sufficient rate of the reaction ofstyrene with isopropanol is generally at least 250° C., frequently atleast 300° C. and especially at least 320° C. To achieve a sufficientselectivity of the reaction, it has been found to be advantageous whenthe temperature of the reaction does not exceed a value of 500° C. Thereaction in step a) is effected preferably at elevated pressure, whichis generally in the range from 5 to 50 MPa, frequently in the range from10 to 30 MPa and especially in the range from 15 to 25 MPa. The pressurein the reaction vessel can be adjusted by charging with an inertsubstance. The reaction is preferably effected under the autogenouspressure of the reaction mixture which exists at the desired reactiontemperature.

By its nature, the reaction time depends on the conditions selected andthe conversion desired, and is typically in the range from 30 sec to 4h, particularly in the range from 3 min to 3 h and especially in therange from 5 min to 2.5 h. In general, the reaction is conducted to suchan extent that the reactant used in deficiency, which is preferablystyrene, is converted to an extent of at least 80%, especially to anextent of at least 90%.

In one embodiment of the invention, the reaction time is in the rangefrom 30 min to 4 h, particularly in the range from 1 to 3 h andespecially in the range from 1.5 to 2.5 h. In general, the reaction isconducted to such an extent that the reactant used in deficiency, whichis preferably styrene, is converted to an extent of at least 80%,especially to an extent of at least 90%.

It has been found to be particularly advantageous to perform thereaction of step a) at elevated temperatures, i.e. above 300° C.,especially above 320° C., especially in the range of 350° C. and 500°C., preferably in the range of 390° C. and 500° C. This allows shortreaction times, which are typically in the range from 30 sec to 30 min,particularly in the range from 3 min to 20 min and especially in therange from 5 min to 15 min. In this way, even at a high styreneconversion, selectivities based on the target product of distinctly >60%can be achieved.

With regard to the selectivity of the reaction, it has been found to beadvantageous when the reaction in step a) is performed in substantial orcomplete absence of catalysts, for example free-radical initiators,acids or transition metal compounds. “Substantial absence” means thatthe concentration of any catalysts is less than 1 g/kg (<1000 ppm),especially less than 0.1 g/kg (<100 ppm), based on the total weight ofthe reaction mixture.

The reaction of styrene with isopropanol in step a) can be performed inbulk or in a suitable diluent, i.e. one which is inert under reactionconditions. Suitable inert diluents are aprotic organic solvents whichdo not have an ethylenically unsaturated double bond, for examplealiphatic and alicyclic ethers having preferably 4, 5 or 6 carbon atoms,aliphatic and cycloaliphatic saturated hydrocarbons having preferably 6to 8 carbon atoms, alkyl esters of aliphatic carboxylic acids havingpreferably 4 to 8 carbon atoms, and mixtures of the aforementionedsolvents. Preference is given to effecting the reaction in step a) insubstance, i.e. essentially no feedstocks other than styrene andisopropanol, for example inert solvents, are used for the reaction.“Essentially” means here that styrene and isopropanol make up at least95% by weight, especially at least 99% by weight, based on the totalamount of the components used in step a). In addition, the reactantsused for the reaction, i.e. styrene and isopropanol, as a result of thepreparation, may comprise small amounts of impurities such as water,ethylbenzene, toluene and the like, in which case the impuritiesgenerally make up less than 5% by weight, especially less than 1% byweight, based on the total amount of the reactants. In particular, thewater content of the reactants used in step a) is not more than 1% byweight, based on the total amount of the reactants.

In the process according to the invention, styrene and isopropanol areused in step a) in a molar ratio of styrene to isopropanol 1:below 5 to1:0.5.

With regard to an efficient reaction regime, it is advantageous whenstyrene and isopropanol are used in step a) in a molar ratio in therange from 1:4.9 to 1:0.5, especially 1:4.5 to 1:0.5, preferably in therange from 1:4 to 1:0.75 especially in the range from 1:3.5 to 1:1.5, orin the range from 1:2 to 1:1, preferably in the range from 1:1.

The reaction in step a) can be performed in batchwise mode, i.e. styreneand isopropanol are initially charged in a suitable reactor in thedesired molar ratio and brought to the desired reaction conditions andheld under reaction conditions until the desired conversion. Thereaction in step a) can also be performed in what is known assemibatchwise mode, i.e. the majority, generally at least 80%, of one orboth reactants is introduced into the reactor under reaction conditionscontinuously or in portions over a prolonged period, generally at least50% of the total reaction time. The reaction in step a) can also beperformed continuously, i.e. styrene and isopropanol are fedcontinuously into a reaction zone in the desired molar ratio and thereaction mixture is withdrawn continuously from the reaction zone. Therate at which styrene and isopropanol are supplied to the reaction zoneis guided by the desired residence time, which in turn depends in aknown manner on the reactor geometry and the above-specified reactiontime.

The reaction in step a) can in principle be performed in all reactorssuitable for the selected reaction conditions, preferably in autoclaves,which may have apparatus for mixing of the reactants, or in reactiontubes.

In order to keep the molar ratio of styrene to isopropanol low duringthe reaction and simultaneously to allow an efficient reaction regime,it has been found to be advantageous when at least 80%, especially atleast 90%, of the isopropanol used in step a) is initially charged,optionally together with a portion of the styrene, and at least 80%,especially at least 90%, of the styrene used in step a) is fed to thereaction in step a) under reaction conditions. The styrene can be addedin portions or preferably continuously. The rate at which styrene is fedin is preferably selected such that the molar ratio of the as yetunreacted styrene fed into the reaction zone or the reactor to theisopropanol present in the reaction zone during the reaction is lessthan 1:below 5, particularly not more than 1:4.9, especially not morethan 1:4.5 and especially not more than 1:4, for example in the rangefrom 1.49 to 1:0.5, especially 1:4.5 to 1:0.5, preferably in the rangefrom 1:4 to 1:0.75 and especially in the range from 1:3.5 to 1:1.5. In acontinuous reaction regime, styrene and isopropanol will thereforepreferably be supplied to the reactor or to the reaction zone in theaforementioned molar ratios. In an embodiment of the invention, the ratewith which styrene is supplied is preferably selected such that themolar ratio of the styrene fed into the reaction zone or the reactor tothe isopropanol present in the reaction zone is in the range from1:below 5, particularly in the range from 1:4.9 to 1:0.5, especially1:4.5 to 1:0.5, especially more preferably in the range from 1:4 to1:0.75 and especially in the range from 1:3.5 to 1:1.5, especially 1:2to 1:1. This is especially true, in the case of a continuous reactionregime too, of the molar ratios of styrene and isopropanol supplied tothe reactor or to the reaction zone.

The present invention further provides a process for preparing2-methyl-4-phenyl-2-butanol, comprising a) the reaction of styrene withisopropanol at elevated temperature, where the molar ratio of thestyrene used in step a) to the isopropanol used in step a) is in therange from 1:below 5 to 1:0.5.

It has been found to be particularly advantageous to perform thereaction of step a) at elevated temperatures, i.e. above 300° C.,especially above 320° C., especially in the range of 350° C. and 500°C., preferably in the range of 390° C. and 500° C.

A preferred embodiment of the invention relates to a process forpreparing 2-methyl-4-phenyl-2-butanol, comprising a) the reaction ofstyrene with isopropanol at elevated temperature, where the molar ratioof the styrene used in step a) to the isopropanol used in step a) is inthe range from 1:below 5 to 1:0.5, and where the temperature is greaterthan or equal to 390° C., especially greater than or equal to 450° C.

For the rest, the preferred reaction conditions specified above understep a) apply to this further subject of the invention.

It has been found that, surprisingly, with the process according to theinvention, it is also possible to employ significantly greater ratios ofstyrene to isopropanol compared to the prior art without occurrence ofany greater conversion or yield losses. This is also enabled by the factthat, with the process according to the invention, unwanted formation ofpolystyrene is reduced—thus, more styrene monomer is available to thereaction, and shifts in the reaction system are prevented.

The reaction mixture obtained in step a) can be worked up in a mannerknown per se or be used directly as such in step b) of the processaccording to the invention. In general, it has been found to beadvantageous to work up the reaction mixture obtained in step a), forexample by extraction or distillation or by a combination of thesemeasures. In one embodiment of the process according to the invention,the reaction mixture obtained in step a) is worked up by distillation toremove the desired 2-methyl-4-phenyl-2-butanol as the medium fractionfrom low and high boilers. When working with an isopropanol excess, thelow boiler fraction consisting predominantly of isopropanol can berecycled into the process. In general, isopropanol will be substantiallyremoved before step b), such that the proportion of isopropanol in thereactant used for hydrogenation in step b) is less than 20% by weight,especially not more than 10% by weight, based on the total amount ofreactant in step b).

According to the configuration of the distillation, puremethyl-4-phenyl-2-butanol is obtained (purity ≧95% by weight,particularly ≧98% by weight and especially ≧99% by weight or ≧99.5% byweight), or a composition which consists essentially, i.e. to an extentof at least 95% by weight, particularly at least 98% by weight andespecially at least 99% by weight or at least 99.5% by weight, of2-methyl-4-phenyl-2-butanol and small amounts of2-methyl-4-phenyl-2-pentanol, for example compositions in which theweight ratio of 2-methyl-4-phenyl-2-butanol to2-methyl-4-phenyl-2-pentanol is in the range from 50:1 to 1000:1. Boththe pure 2-methyl-4-phenyl-2-butanol and the composition which consistsessentially of 2-methyl-4-phenyl-2-butanol and small amounts of2-methyl-4-phenyl-2-pentanol can be used in the subsequent hydrogenationin step b), and give correspondingly pure4-cyclohexyl-2-methyl-2-butanol (purity 95% by weight, particularly 98%by weight and especially ≧99% by weight or ≧99.5% by weight), or acomposition which consists essentially, i.e. to an extent of at least95% by weight, particularly at least 98% by weight and especially atleast 99% by weight or at least 99.5% by weight of4-cyclohexyl-2-methyl-2-butanol, and small amounts of4-cyclohexyl-2-methyl-2-pentanol, for example compositions in which theweight ratio of 4-cyclohexyl-2-methyl-2-butanol to4-cyclohexyl-2-methyl-2-pentanol is in the range from 50:1 to 1000:1.

The 2-methyl-4-phenyl-2-butanol obtained in step a) is subsequentlysubjected, in step b) of the process according to the invention, to aheterogeneously catalyzed hydrogenation over a catalyst suitable forring hydrogenation of aromatics, which is also referred to hereinafteras catalyst.

Suitable catalysts are in principle all catalysts known to be suitablefor ring hydrogenation of aromatics, i.e. catalysts which catalyze thehydrogenation of phenyl groups to cyclohexyl groups. These are typicallycatalysts which comprise at least one active metal from group VIIIB ofthe Periodic Table (CAS version), for example palladium, platinum, iron,cobalt, nickel, rhodium, iridium, ruthenium, especially ruthenium,rhodium or nickel, or a mixture of two or more thereof, optionally incombination with one or more further active metals. Preferred furtheractive metals are selected from groups IB and VIIIB of the PeriodicTable (CAS version). Among the likewise usable metals of transitiongroups IB and/or VIIB of the Periodic Table of the Elements, forexample, copper and/or rhenium are suitable.

The catalysts may be unsupported catalysts or preferably supportedcatalysts. Suitable support materials are, for example, activatedcarbon, silicon carbide, silicon dioxide, aluminum oxide, magnesiumoxide, titanium dioxide, zirconium dioxide, aluminosilicates andmixtures of these support materials. The amount of active metal istypically 0.05 to 10% by weight, frequently 0.1 to 7% by weight andespecially 4 to 7% by weight, preferably 5 to 7% by weight, based on thetotal weight of the supported catalyst, especially when the active metalis a noble metal such as rhodium, ruthenium, platinum, palladium oriridium. In catalysts which comprise cobalt and/or nickel as activemetals, the amount of active metal may be up to 100% by weight and istypically in the range from 1 to 100% by weight, especially 10 to 90% byweight, based on the total weight of the catalyst.

The supported catalysts can be used in the form of a powder. In general,such a powder has particle sizes in the range from 1 to 200 μm,especially 1 to 100 μm. Pulverulent catalysts are suitable especiallywhen the catalyst is suspended in the reaction mixture to behydrogenated (suspension mode). In the case of use of the catalysts infixed catalyst beds, it is customary to use shaped bodies, which mayhave, for example, the shape of spheres, tablets, cylinders, strands,rings or hollow cylinders, stars and the like. The dimensions of theseshaped bodies vary typically within the range from 0.5 mm to 25 mm.Frequently, catalyst extrudates with extrudate diameters of 1.0 to 5 mmand extrudate lengths of 2 to 25 mm are used. It is generally possibleto achieve higher activities with smaller extrudates, but thesetypically do not have sufficient mechanical stability in thehydrogenation process. Therefore, very particular preference is given tousing extrudates with extrudate diameters in the range from 1.5 to 3 mm.Likewise preferred are spherical support materials with sphere diametersin i the range from 1 to 10 mm, especially 2 to 6 mm.

Preferred catalysts are those which comprise at least one active metalselected from ruthenium, rhodium and nickel, and optionally incombination with one or more further active metals selected from groupsIB, VIIB or VIIIB of the Periodic Table (CAS version).

Particularly preferred catalysts are ruthenium catalysts. These compriseruthenium as the active metal, optionally in combination with one ormore further active metals.

Preferred further active metals are selected from groups IB, VIIB orVIIIB of the Periodic Table (CAS version). The catalysts are unsupportedcatalysts or preferably supported catalysts. Examples of further activemetals from group VIIIB are, for example, platinum, rhodium, palladium,iridium, iron, cobalt or nickel, or a mixture of two or more thereof.Among the likewise usable metals of transition groups IB and/or VIIB ofthe Periodic Table of the Elements, for example, copper and/or rheniumare suitable. Preference is given to using ruthenium alone as the activemetal, or together with platinum or iridium as the active metal; veryparticular preference is given to using ruthenium alone as the activemetal.

Preference is given especially to ruthenium catalysts in which theruthenium is arranged on support material, called supported rutheniumcatalysts. The support materials of such supported catalysts generallyhave a BET surface area, determined by N₂ adsorption to DIN 66131, of atleast 30 m²/g, especially 50 to 1500 m²/g, preferably 800 to 1200 m²/g.Preference is given to silicon dioxide-containing support materials,especially those which have a silicon dioxide content of at least 90% byweight, based on the total weight of the support material. Likewisepreferred are aluminum oxide-containing support materials, especiallythose which have an aluminum oxide content (calculated as Al₂O₃) of atleast 90% by weight, based on the total weight of the support material.Activated carbon support materials are likewise preferred, these beingcommercially available, for example, under the “Norit SX plus” tradename from Norit.

Suitable ruthenium catalysts are the catalysts specified, for example,in U.S. Pat. No. 3027398, DE 4407091, EP 258789, EP 813906, EP 1420012,WO 99/32427, WO 00/78704, WO 02/100536, WO 03/103830, WO 2005/61105, WO2005/61106, WO 2006/136541, EP 1317959, and that specified in EP09179201.0, which was yet to be published at the priority date of thepresent application. With regard to the catalysts disclosed therein,reference is made to these documents.

Equally preferred catalysts are rhodium catalysts. These compriserhodium as an active metal, optionally in combination with one or morefurther active metals. Preferred further active metals are selected fromgroups IB, VIIB or VIIIB of the Periodic Table (CAS version). Thecatalysts may be unsupported catalysts or preferably supportedcatalysts. Examples of further active metals are from the group VIIIBare, for example, platinum, palladium, iridium, iron, cobalt or nickel,or a mixture of two or more thereof. Among the likewise useable metalsof transition groups IB and/or VIIB of the Periodic Table of theElements, copper and/or rhenium, for example, are suitable. In thesecatalysts, preference is given to using rhodium alone as the activemetal. Suitable rhodium catalysts are known, for example, from thepublications cited above for ruthenium catalysts, or can be prepared bythe procedures specified therein, or are commercially available, forexample the catalyst Escat 34 from Engelhard.

Equally preferred catalysts are nickel catalysts. These comprise nickelas an active metal, optionally in combination with one or more furtheractive metals. Preferred further active metals are selected from groupsIB, VIIIB or VIIIB of the Periodic Table (CAS version). The catalystsmay be unsupported catalysts or preferably supported catalysts. Examplesof further active metals are from the group VIIIB are, for example,platinum, palladium, iridium, iron or cobalt, or a mixture of two ormore thereof. Among the likewise useable metals of transition groups IBand/or VIIB of the Periodic Table of the Elements, copper and/orrhenium, for example, are suitable. In these catalysts, preference isgiven to using nickel alone as the active metal. Suitable nickelcatalysts are commercially available, for example BASF catalyst Ni5249P.

The catalyst used in step b) is more preferably a supported catalystwhich comprises, as an active metal, ruthenium alone or together with atleast one further active metal of transition groups IB, VIIIB or VIIIBof the Periodic Table of the Elements (CAS version) on a supportmaterial. Preference is given to using ruthenium alone as the activemetal or together with iron, platinum or iridium as the active metal;very particular preference is given to using ruthenium alone or in acombination with iron as the active metal. Useful support materials forthe supported ruthenium catalysts are in principle the aforementionedsupport materials. Preference is given to silicon dioxide-containingsupport materials, especially those which have a silicon dioxide contentof at least 90% by weight, based on the total weight of the supportmaterial. Preference is likewise given to aluminum oxide-containingsupport materials, especially those which have an aluminum oxide content(calculated as Al₂O₃) of at least 90% by weight, based on the totalweight of the support material. Preference is given to support materialshaving a specific BET surface area, determined by N₂ adsorption to DIN66131, of at least 30 m²/g, especially 50 to 1500 m²/g, especially 800to 1200 m²/g. The amount of active metal is typically 0.05 to 10% byweight, preferably 0.1 to 3% by weight and especially 0.1 to 1% byweight, based on the total weight of the supported ruthenium catalyst.Activated carbon support materials are likewise preferred, these beingcommercially available, for example, under the “Norit SX plus” tradename from Norit.

Likewise preferably, the catalyst used in step b) is a supportedcatalyst which comprises, as an active metal, rhodium alone or togetherwith at least one further active metal of transition groups IB, VIIB orVIIIB of the Periodic Table of the Elements (CAS version) on a supportmaterial. Preference is given to using rhodium alone as the active metalor together with platinum or iridium as the active metal; veryparticular preference is given to using rhodium alone as the activemetal. Useful support materials for the supported rhodium catalysts arein principle the aforementioned support materials. Preference is givento silicon dioxide-containing support materials, especially those whichhave a silicon dioxide content of at least 90% by weight, based on thetotal weight of the support material. Preference is likewise given toaluminum oxide-containing support materials, especially those which havealuminum oxide content (calculated as Al₂O₃) of at least 90% by weight,based on the total weight of the support material. The amount of activemetal is typically 0.05 to 10% by weight, based on the total weight ofthe supported rhodium catalyst.

Likewise preferably, the catalyst used in step b) is a catalyst whichcomprises, as an active metal, nickel alone or together with at leastone further active metal of transition groups IB, VIIB or VIIIB of thePeriodic Table of the Elements (CAS version), optionally on a supportmaterial. Preference is given to using nickel alone as the active metal.Useful support materials for the supported nickel catalysts are inprinciple the aforementioned support materials. Preference is given tosilicon dioxide-, aluminum oxide- and magnesium oxide-containing supportmaterials, especially those which consist to an extent of at least 90%by weight of such materials. The amount of active metal is typically 1to 90% by weight, preferably 10 to 80% by weight and especially 30 to70% by weight, based on the total weight of the supported nickelcatalyst. Preference is also given to those nickel catalysts whichconsist essentially exclusively of active metal, i.e. wherein the amountof active metal is more than 90% by weight, e.g. 90 to 100% by weight.

In a particularly preferred embodiment, a shell catalyst is used,especially a shell catalyst which has, as the active metal, rutheniumalone or together with at least one further active metal of transitiongroups IB, VIIB or VIIIB of the Periodic Table of the Elements in theamounts specified above. Such shell catalysts are known especially fromWO 2006/136541, and in EP 09179201.0, which was yet to be published atthe priority date of the present application.

Such a shell catalyst is a supported catalyst wherein the predominantamount of the active metals) present in the catalyst is close to thesurface of the catalyst. In particular, at least 60% by weight, morepreferably at least 80% by weight, based in each case on the totalamount of the active metal, is present down to a penetration depth ofnot more than 200 μm, i.e. in a shell with a distance of not more than200 μm from the surface of the catalyst particles. In contrast, only avery small amount, if any, of the active metal is present in theinterior (core) of the catalyst. Very particular preference is given toan inventive shell catalyst in which no active metal can be detected inthe interior of the catalyst, i.e. active metal is present only in theoutermost shell, for example in a zone down to a penetration depth of100 to 200 μm. The aforementioned data can be determined by means of SEM(scanning electron microscopy), EPMA (electron probe microanalysis)—EDXS(energy dispersive X-ray spectroscopy), and are averaged values. Furtherdata with regard to the aforementioned test methods and techniques canbe found, for example, in “Spectroscopy in Catalysis” by J. W.Niemantsverdriet, VCH, 1995. For further details regarding thepenetration depth of active metal, reference is made to WO 2006/136541,especially to page 7 lines 6 to 12.

Preferred shell catalysts have a content of active metal in the rangefrom 0.05 to 1% by weight, especially 0.1 to 0.5% by weight, morepreferably 0.25 to 0.35% by weight, based in each case on the totalweight of the catalyst.

For the inventive hydrogenation in step b), particular preference isgiven to shell catalysts with a support material based on silicondioxide, generally amorphous silicon dioxide. The term “amorphous” inthis context is understood to mean that the proportion of crystallinesilicon dioxide phases makes up less than 10% by weight of the supportmaterial. The support materials used to prepare the catalysts may,however, have superstructures which are formed via regular arrangementof pores in the support material. Useful support materials are inprinciple amorphous silicon dioxide types which consist at least to anextent of 90% by weight of silicon dioxide, where the remaining 10% byweight, preferably not more than 5% by weight, of the support materialmay also be another oxidic material, for example MgO, CaO, TiO₂, ZrO₂,Fe₂O₃ and/or alkali metal oxide. In a preferred embodiment of the shellcatalyst, the support material is halogen-free, especiallychlorine-free, i.e. the content of halogen in the support material isless than 500 ppm by weight, for example in the range from 0 to 400 ppmby weight. Thus, a preferred shell catalyst is one which comprises lessthan 0.05% by weight of halide (determined by ion chromatography), basedon the total weight of the catalyst. Preference is given to supportmaterials which have a specific surface area in the range from 30 to 700m²/g, preferably 30 to 450 m²/g (BET surface area to DIN 66131).Suitable amorphous support materials based on silicon dioxide arefamiliar to those skilled in the art and are commercially available(see, for example, O. W. Flörke, “Silica” in Ullmann's Encyclopedia ofIndustrial Chemistry, 6th Edition on CD-ROM). They may either be ofnatural origin or may have been produced synthetically. Examples ofsuitable amorphous support materials based on silicon dioxide are silicagels, kieselguhr, fumed silicas and precipitated silicas. In a preferredembodiment of the invention, the catalysts have silica gels as supportmaterials. According to the configuration of the shell catalyst, thesupport material may have different shapes. When the process in whichthe inventive shell catalysts are used is configured as a suspensionprocess, the inventive catalysts will typically be prepared using thesupport material in the form of a fine powder. The powder preferably hasparticle sizes in the range from 1 to 200 μm, especially 1 to 100 μm. Inthe case of use of the inventive shell catalyst in fixed catalyst beds,it is customary to use shaped bodies of the support material, which areobtainable, for example, by extrusion or tableting, and which may have,for example, the form of spheres, tablets, cylinders, extrudates, ringsor hollow cylinders, stars and the like. The dimensions of these shapedbodies typically vary within the range from 0.5 mm to 25 mm. Frequently,catalyst extrudates with extrudate diameters of 1.0 to 5 mm andextrudate lengths of 2 to 25 mm are used. It is generally possible toachieve higher activities with smaller extrudates; these, however, oftendo not have sufficient mechanical stability in the hydrogenationprocess. Therefore, very particular preference is given to usingextrudates with extrudate diameters in the range from 1.5 to 3 mm.Preference is likewise given to spherical support materials with spherediameters in the range from 1 to 10 mm, especially 2 to 6 mm.

In a particularly preferred embodiment of the shell catalysts, thesupport material of the catalyst, which is especially a support materialbased on silicon dioxide, has a pore volume in the range from 0.6 to 1.0ml/g, preferably in the range from 0.65 to 0.9 ml/g, for example 0.7 to0.8 ml/g, determined by Hg porosimetry (DIN 66133), and a BET surfacearea in the range from 280 to 500 m²/g, preferably in the range from 280to 400 m²/g, most preferably in the range from 300 to 350 m²/g. In suchshell catalysts, at least 90% of the pores present preferably have adiameter of 6 to 12 nm, preferably 7 to 11 nm, more preferably 8 to 10nm. The pore diameter can be determined by processes known to thoseskilled in the art, for example by Hg porosimetry or N₂ physisorption.In a preferred embodiment, at least 95%, more preferably at least 98%,of the pores present have a pore diameter of 6 to 12 nm, preferably 7 to11 nm, more preferably 8 to 10 nm. In a preferred embodiment, no poressmaller than 5 nm are present in these shell catalysts. Furthermore,there are preferably no pores larger than 25 nm, especially larger than15 nm, in these shell catalysts. In this composition, “no pores” meansthat no pores with these diameters can be found by customary testmethods, for example Hg porosimetry or N₂ physisorption.

In preferred shell catalysts, the dispersity of the active metal ispreferably 30 to 60%, more preferably 30 to 50%. Processes for measuringthe dispersity of the active metal are known per se to those skilled inthe art, for example by pulse chemisorption, the determination of thenoble metal dispersion (specific metal surface area, crystal size) beingcarried out by the CO pulse method (DIN 66136(1-3)).

The hydrogenation process according to the invention can be performed inthe liquid phase or in the gas phase. Preference is given to performingthe hydrogenation process according to the invention in the liquidphase.

The hydrogenation process according to the invention can be performed inthe absence of a solvent or diluent or in the presence of a solvent ordiluent, i.e. it is not necessary to perform the hydrogenation insolution. The solvent or diluent used may be any suitable solvent ordiluent. Useful solvents or diluents are in principle those which arecapable of very substantially dissolving the organic compounds to behydrogenated, or mix completely therewith, and which are inert under thehydrogenation conditions, i.e. are not hydrogenated. Examples ofsuitable solvents are cyclic and acyclic ethers having preferably 4 to 8carbon atoms, for example tetrahydrofuran, dioxane, methyl tert-butylether, dimethoxyethane, dimethoxypropane, dimethyldiethylene glycol,aliphatic alcohols having preferably 1 to 6 carbon atoms, such asmethanol, ethanol, n- or isopropanol, n-, 2-, iso- or tert-butanol,carboxylic esters of aliphatic carboxylic acids having preferably 3 to 8carbon atoms, such as methyl acetate, ethyl acetate, propyl acetate orbutyl acetate, methyl propionate, ethyl propionate, butyl propionate,and aliphatic ether alcohols such as methoxypropanol, and cycloaliphaticcompounds such as cyclohexane, methylcyclohexane anddimethylcyclohexane. The amount of the solvent or diluent used is notparticularly restricted and can be selected freely as required,although, when using a solvent, preference is given to those amountswhich lead to a 3 to 70% by weight solution of the organic compoundintended for hydrogenation.

In one embodiment of the invention, step b) of the invention isperformed in substance.

The actual hydrogenation is effected typically in analogy to the knownhydrogenation processes for hydrogenating organic compounds which havehydrogenatable groups, preferably for hydrogenating a carbocyclicaromatic group to the corresponding carbocyclic aliphatic group, asdescribed in the prior art cited at the outset. For this purpose, theorganic compound as a liquid phase or gas phase, preferably as a liquidphase, is contacted with the catalyst in the presence of hydrogen. Theliquid phase can be passed over a moving catalyst bed (moving bed mode)or a fixed catalyst bed (fixed bed mode).

The hydrogenation can be configured either continuously or batchwise,preference being given to the continuous process regime. The processaccording to the invention is preferably performed in trickle reactorsor in flooded mode by the fixed bed mode, particular preference beinggiven to performance in trickle reactors. More particularly, thecompound to be hydrogenated here is used in substance, i.e. substantialabsence of organic diluents (solvent content preferably<10%). Thehydrogenation can be passed over the catalyst either in cocurrent withthe solution of the reactant to be hydrogenated or in countercurrent.The hydrogenation can also be performed batchwise in batchwise mode. Inthis case, the hydrogenation will preferably be performed in an organicsolvent or diluent.

In a further embodiment of the invention the hydrogenation can beconducted in suspension mode, especially in continuous suspension mode.

In the case of batchwise performance of the process according to theinvention, in step B, the catalyst is typically used in an amount suchthat the concentration of ruthenium in the reaction mixture used forhydrogenation is in the range from 10 to 10 000 ppm, especially in therange from 50 to 5000 ppm, especially in the range from 100 to 1000 ppm.

The hydrogenation is effected typically at a hydrogen pressure in therange from 5 to 50 MPa, especially in the range from 10 to 30 MPa. Thehydrogen can be fed into the reactor as such, or diluted with an inert,for example nitrogen or argon.

The hydrogenation in step b) is effected typically at temperatures above50° C., especially in the range from 100 to 250° C.

Apparatus suitable for performing the hydrogenation is known to thoseskilled in the art and is guided primarily by the mode of operation.Suitable apparatus for performing a hydrogenation according to thehydrogenation over a moving catalyst bed and over a fixed catalyst bedare known, for example, from Ullmanns Enzyklopadie der TechnischenChemie, 4th edition, volume 13, p. 135 ff., and from P. N. Rylander,“Hydrogenation and Dehydrogenation” in Ullmann's Encyclopedia ofIndustrial Chemistry, 5th ed. on CD-ROM.

It has been found that, surprisingly, step a) of the process accordingto the invention affords not only 2-methyl-4-phenyl-2-butanol but also2-methyl-4-phenyl-2-pentanol when it is performed under conditions underwhich isopropanol is present under supercritical conditions, especiallywhen the molar ratio of styrene to isopropanol is in the range from1:below 5 to 1:0.5, particularly in the range from 1:4.9 to 1:0.5especially 1:4.5 to 1:0.5, more preferably in the range from 1:4 to1:0.75 and especially in the range from 1:3.5 to 1:1.5, especially 1:2to 1:1. In a preferred embodiment, the process according to theinvention is performed in semibatchwise mode.

Such a process is novel and likewise forms part of the subject matter ofthe present invention. Accordingly, the invention relates to a processfor preparing a composition comprising 2-methyl-4-phenyl-2-butanol and2-methyl-4-phenyl-2-pentanol, comprising the reaction of styrene withisopropanol at elevated temperature under conditions under whichisopropanol is present under supercritical conditions, the molar ratioof styrene to isopropanol being in the range from 1:below 10, preferably1:9 to 1:0.5, preferably 1:5 to 1:0.5, particularly in the range from1:4.5 to 1:0.5, more preferably in the range from 1:4 to 1:0.75 andespecially in the range from 1:3.5 to 1:1.5, especially 1:2 to 1:1.

It has been found to be advantageous when the reaction is performed insemibatchwise mode or continuously, as already described above for stepa). For this purpose, it has been found to be especially advantageouswhen at least 80%, especially at least 90%, of the isopropanol used isinitially charged, optionally together with a portion of the styrene,and at least 80%, especially at least 90%, of the styrene used issupplied to the reaction under reaction conditions. The styrene can beadded in portions or preferably continuously. The rate with which thestyrene is supplied is preferably selected such that the molar ratio ofthe styrene fed into the reaction zone or the reactor to the isopropanolpresent in the reaction zone is in the range from 1:below 10, preferably1:9 to 1:0.5, preferably 1:5 to 1:0.5, particularly in the range from1:4.5 to 1:0.5, more preferably in the range from 1:4 to 1:0.75 andespecially in the range from 1:3.5 to 1:1.5, especially 1:2 to 1:1. Thisis especially true, in a continuous reaction regime too, of the molarratios of styrene and isopropanol supplied to the reactor or to thereaction zone.

Otherwise, the conditions specified above for step a) also apply in thesame way to the process according to the invention for preparing acomposition comprising 2-methyl-4-phenyl-2-butanol and2-methyl-4-phenyl-2-pentanol. Reference is therefore made to thesedetails in full.

Such a process affords compositions which comprise2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanol. The weightratio of 2-methyl-4-phenyl-2-butanol to 2-methyl-4-phenyl-2-pentanol insuch compositions is typically in the range from 50:1 to 1000:1.

The reaction mixture obtained in the preparation of a compositioncomprising 2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanolby reaction of styrene with isopropanol can be worked up in the mannerdescribed above for step a). Reference is made completely to the detailsgiven above for workup of the reaction mixture obtained in step a). Moreparticularly, the reaction mixture obtained is worked up bydistillation, in which case the desired composition consistingessentially of 2-methyl-4-phenyl-2-butanol and2-methyl-4-phenyl-2-pentanol is removed as the middle fraction from lowand high boilers. In general, a composition is then obtained whichconsists essentially, i.e. to an extent of at least 95% by weight,particularly at least 98% by weight and especially at least 99% byweight or at least 99.5% by weight of 2-methyl-4-phenyl-2-butanol, andsmall amounts of 2-methyl-4-phenyl-2-pentanol, for example compositionsin which the weight ratio of 2-methyl-4-phenyl-2-butanol to2-methyl-4-phenyl-2-pentanol in the range from 50:1 to 1000:1.

Such mixtures of 2-methyl-4-phenyl-2-butanol and small amounts of2-methyl-4-phenyl-2-pentanol can subsequently be hydrogenated in analogyto step b) to obtain compositions comprising4-cyclohexyl-2-methyl-2-butanol and small amounts of4-cyclohexyl-2-methyl-2-pentanol, for example compositions in which theweight ratio of 4-cyclohexyl-2-methyl-2-butanol to4-cyclohexyl-2-methyl-2-pentanol is in the range from 50:1 to 1000:1.Reference is made completely to the details given above for thehydrogenation in step b). Since, in one embodiment of the invention, anisopropanol excess can be employed in the preparation of a compositioncomprising 2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanol,the low boiler fraction, which consists predominantly of isopropanol,can be recycled into the process in this embodiment. In general,isopropanol will be substantially removed before the hydrogenation, suchthat the proportion of isopropanol in the reactant used for thehydrogenation is less than 20% by weight, especially not more than 10%by weight, based on the total amount of reactant.

Compositions comprising 2-methyl-4-phenyl-2-butanol and2-methyl-4-phenyl-2-pentanol are surprisingly notable in that they havea more flowery odor note compared to 2-methyl-4-phenyl-2-butanol. Inthese compositions, the weight ratio of 2-methyl-4-phenyl-2-butanol to2-methyl-4-phenyl-2-pentanol is in the range from 50:1 to 1000:1. Aspecific composition is that of concentrates, i.e. compositions whichconsist essentially, i.e. to an extent of at least 95% by weight,particularly at least 98% by weight and especially at least 99% byweight or at least 99.5% by weight of 2-methyl-4-phenyl-2-butanol andsmall amounts of 2-methyl-4-phenyl-2-pentanol, for example compositionsin which the weight ratio of 2-methyl-4-phenyl-2-butanol to2-methyl-4-phenyl-2-pentanol is in the range from 50:1 to 1000:1.Compositions in which the weight ratio of 2-methyl-4-phenyl-2-butanol to2-methyl-4-phenyl-2-pentanol is outside the range specified here can beprepared by mixing 2-methyl-4-phenyl-2-butanol (Muguet alcohol) with thedesired amount of 2-methyl-4-phenyl-2-pentanol.

Such compositions, especially the aforementioned concentrates, can beused as fragrances or aromas for the reasons mentioned above, especiallyin cosmetic compositions and in washing or cleaning compositions.

It has additionally been found in the context of this invention that2-methyl-4-phenyl-2-pentanol can also be prepared in a controlled mannerby reacting α-methylstyrene with isopropanol under the conditionsspecified above for step a).

The invention therefore also provides a process for preparing2-methyl-4-phenyl-2-pentanol, in which α-methylstyrene is reacted withisopropanol at elevated temperature, where the molar ratio of theα-methylstyrene used to the isopropanol used is in the range from1:below 5 to 1:0.5, preferably in the range from 1:4.9 to 1:0.5,particularly in the range from 1:4.5 to 1:0.5, more preferably in therange from 1:4 to 1:0.75 and especially in the range from 1:3.5 to1:1.5, especially 1:2 to 1:1.

For the reaction of α-methylstyrene with isopropanol, essentially alldetails apply which have been given above and in the claims for thereaction of styrene with isopropanol in step a). Reference is thereforemade completely to these details.

Alternatively, 2-methyl-4-phenyl-2-pentanol or a mixture consistingessentially of 2-methyl-4-phenyl-2-pentanol can be obtained bydistillative separation of mixtures comprising2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanol, forexample by distillative separation of mixtures as obtained in step a) ofthe process according to the invention.

2-Methyl-4-phenyl-2-pentanol is likewise an odorant and can therefore beused in all applications for odorants of this type. As already statedabove, it can surprisingly also be used for modification of the odorproperties of 2-methyl-4-phenyl-2-butanol.

2-Methyl-4-phenyl-2-pentanol can be subjected to a hydrogenation inanalogy to step b). This gives 4-cyclohexyl-2-methyl-2-pentanol in ahigh yield.

4-Cyclohexyl-2-methylpentanol is, similarly to4-cyclohexyl-2-methyl-2-butanol, an odorant. In addition, it cansurprisingly be used for modification of the odor properties of otherodorants, especially of 4-cyclohexyl-2-methyl-2-butanol.4-Cyclohexyl-2-methyl-2-pentanol can therefore be used as a fragrance oraroma, especially in cosmetic compositions and in washing or cleaningcompositions.

In these compositions, the weight ratio of4-cyclohexyl-2-methyl-2-butanol to 4-cyclohexyl-2-methyl-2-pentanol isgenerally in the range from 50:1 to 1000:1. Such compositions may alsocomprise small amounts of 4-cyclohexyl-2-methylbutane and possibly4-cyclohexyl-2-methylpentane, which are obtained by over-reduction of2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanolrespectively. The proportion by weight of the total amount ofcyclohexyl-2-methylbutane and any 4-cyclohexyl-2-methylpentane willgenerally not exceed 10% by weight, especially 5% by weight, based on4-cyclohexyl-2-methyl-2-butanol, and is, if present, in the range from0.01 to 10% by weight, especially in the range from 0.01 to 5% byweight, based on 4-cyclohexyl-2-methyl-2-butanol. It is of course alsopossible to remove cyclohexyl-2-methylbutane and any4-cyclohexyl-2-methylpentane, for example by a distillative route, suchthat the total amount of cyclohexyl-2-methylbutane and any4-cyclohexyl-2-methylpentane is less than 1% by weight, especially lessthan 0.5% by weight or less than 0.1% by weight, based on4-cyclohexyl-2-methyl-2-butanol. A specific composition is that ofconcentrates, i.e. compositions which consist essentially, i.e. to anextent of at least 95% by weight, particularly at least 98% by weightand especially at least 99% by weight or at least 99.5% by weight of4-cyclohexyl-2-methyl-2-butanol and small amounts of4-cyclohexyl-2-methyl-2-pentanol, for example compositions in which theweight ratio of 4-cyclohexyl-2-methyl-2-butanol to4-cyclohexyl-2-methyl-2-pentanol is in the range from 50:1 to 1000:1.

These concentrates may comprise cyclohexyl-2-methylbutane and possibly4-cyclohexyl-2-methylpentane in the amounts mentioned above.Compositions in which the weight ratio of4-cyclohexyl-2-methyl-2-butanol to 4-cyclohexyl-2-methyl-2-pentanol isoutside the range specified here can be prepared by mixingcyclohexyl-2-methyl-2-butanol with the desired amount of4-cyclohexyl-2-methyl-2-pentanol.

Such compositions, especially the aforementioned concentrates, can beused as fragrances or aromas for the reasons mentioned above, especiallyin cosmetic compositions and in washing or cleaning compositions.

As already stated above, 4-cyclohexyl-2-methyl-2-pentanol can beprepared from 2-methyl-4-phenyl-2-pentanol in analogy to step b), i.e.by a process comprising a heterogeneously catalyzed hydrogenation of2-methyl-4-phenyl-2-pentanol over a catalyst suitable for ringhydrogenation of aromatics. Such a process likewise forms part of thesubject matter of the present invention. With regard to thehydrogenation of 2-methyl-4-phenyl-2-pentanol, reference is madecompletely to the details given above for the hydrogenation in step b).

The procedure here may be first to prepare 2-methyl-4-phenyl-2-pentanolin a controlled manner and then to subject it to a heterogeneouslycatalyzed hydrogenation over a catalyst suitable for ring hydrogenationof aromatics, in analogy to step b) described above.

However, the procedure may also be first to prepare a compositioncomposed of 2-methyl-4-phenyl-2-butanol and2-methyl-4-phenyl-2-pentanol, for example in the manner described abovefor step a), to subject this composition to a heterogeneously catalyzedhydrogenation over a catalyst suitable for ring hydrogenation ofaromatics in analogy to the above-described step b), and to separate thecomposition obtained, which comprises 4-cyclohexyl-2-methyl-2-butanoland 4-cyclohexyl-2-methyl-2-pentanol, into its constituents bydistillation.

Accordingly, the invention also relates to a process for preparing4-cyclohexyl-2-methyl-2-pentanol, comprising the following steps:

-   -   a′) preparation of a composition comprising        2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanol by        reaction of styrene with isopropanol at elevated temperature        under conditions under which isopropanol is present under        supercritical conditions, the molar ratio of styrene to        isopropanol being in the range from 1:below 10 to 1:0.5,        preferably in the range from 1:9 to 1:0.5, particularly in the        range from 1:5 to 1:0.5, especially in the range from 1:4.5 to        1:0.5, more preferably in the range from 1:4 to 1:0.75 and        especially in the range from 1:3.5 to 1:1.5, especially 1:2 to        1:1;    -   b′) heterogeneously catalyzed hydrogenation of the composition        obtained in step a) over a catalyst suitable for ring        hydrogenation of aromatics; and    -   c) distillative workup of the composition obtained in step b′)        to obtain a composition consisting essentially, i.e. to an        extent of at least 90% by weight, especially to an extent of at        least 95% by weight, of 4-cyclohexyl-2-methyl-2-pentanol.

Accordingly, the invention further relates to a process for preparing4-cyclohexyl-2-methyl-2-pentanol, comprising the following steps:

-   -   a′) preparation of a composition comprising        2-methyl-4-phenyl-2-butanol and 2-methyl-4-phenyl-2-pentanol by        reaction of styrene with isopropanol at elevated temperature        under conditions under which isopropanol is present under        supercritical conditions, the molar ratio of styrene to        isopropanol being in the range from 1:below 10 to 1:0.5,        preferably in the range from 1:9 to 1:0.5, particularly in the        range from 1:5 to 1:0.5, especially in the range from 1:4.5 to        1:0.5, more preferably in the range from 1:4 to 1:0.75 and        especially in the range from 1:3.5 to 1:1.5, especially 1:2 to        1:1.    -   c′) distillative workup of the composition obtained in step a′)        to obtain a composition consisting predominantly of        2-methyl-4-phenyl-2-pentanol    -   b′) heterogeneously catalyzed hydrogenation of the composition        obtained in step c′) over a catalyst suitable for ring        hydrogenation of aromatics; and optionally    -   c″) distillative workup of the composition obtained in step b′)        to obtain a composition consisting essentially of        4-cyclohexyl-2-methyl-2-pentanol.

It will be appreciated that step a′) is performed in analogy to the stepa) already described above. To that extent, for step a′), reference ismade completely to the details given for step a).

It will also be appreciated that step b′) is performed in analogy to thestep ab) already described above. To that extent, for step b′),reference is made completely to the remarks made for step b).

The distillative steps c), c′) and c″) can be performed in analogy tocustomary processes for fractional distillation. Suitable apparatus forthis purpose is familiar to those skilled in the art. The necessaryconditions can be determined by routine experiments. In general,distillation is effected under reduced pressure.

In addition, the invention additionally relates to a process forpreparing 4-cyclohexyl-2-methyl-2-pentanol, comprising the followingsteps:

-   -   a″) reaction of α-methylstyrene with isopropanol at elevated        temperature to obtain 2-methyl-4-phenyl-2-pentanol, and    -   b″) heterogeneously catalyzed hydrogenation of        2-methyl-4-phenyl-2-pentanol over a catalyst suitable for ring        hydrogenation of aromatics,        where the molar ratio of the α-methylstyrene used in step a″) to        the isopropanol used in step a″) is in the range from 1:below 5        to 1:0.5, preferably in the range from 1:4.9 to 1:0.5,        particularly in the range from 1:4.5 to 1:0.5, more preferably        in the range from 1:4 to 1:0.75 and especially in the range from        1:3.5 to 1:1.5, especially 1:2 to 1:1.

As already explained above, step a″) is performed in analogy to the stepa) already described above. To that extent, for step a″), reference ismade completely to the details given for step a).

It will also be appreciated that step b″) is performed in analogy to thestep ab) already described above. To that extent, for step b″),reference is made completely to the details given for step b).

It will also be appreciated that the reaction product obtainable in stepa″), before use thereof in step b″), can be subjected to a workup inanalogy to that for the reaction product obtained in step a) above,especially to a distillative workup in which low boilers and highboilers are removed, and 2-methyl-4-phenyl-2-pentanol is obtained as amedium boiler. In this regard, reference is likewise made to the detailsgiven above.

Preparation example 1: Preparation of the hydrogenation catalyst

The support material used was a spherical SiO₂ support (AF125 type fromBASF SE) with a sphere diameter of 3 to 5 mm and a tapped density of0.49 kg/I. The BET surface area was 337 m²/g, and the water absorption(WA) 0.83 ml/g. For impregnation, 14.25% by weight ruthenium(III)acetate solution in acetic acid from Umicore was used.

200 g of support were initially charged in a round-bottom flask. 15 g ofruthenium acetate solution were diluted with distilled water to 150 ml(90% WA). The support material was initially charged in the distillationflask of a rotary evaporator, and the first quarter of the solution waspumped onto the support material at 3 to 6 rpm with a slightly reducedpressure. On completion of the addition, the support was left in therotary evaporator at 3 to 6 rpm for a further 10 minutes, in order tohomogenize the catalyst. This impregnation-homogenization step wasrepeated three times more until all of the solution had been applied tothe support. The support material thus treated was dried while beingagitated in the rotary tube oven at 140° C., then reduced in a hydrogenstream (20 l/h of H₂; 10 l/h of N₂) at 200° C. for 3 h, and passivatedat 25° C. (5% air in N₂, 2 h). The inventive catalyst A thus obtainedcomprised 0.34% by weight of ruthenium, based on the catalyst weight.

EXAMPLE 1

Step a)

The reaction was performed in a continuous laboratory plant which, as areactor, comprised a 300 ml autoclave which was operated with pressureregulation. Thus, the amount withdrawn at any time corresponded to theamount introduced. The reaction mixture withdrawn was cooled,decompressed and collected in a discharge vessel.

A solution of styrene in isopropanol (30% by weight, 200 g/h) was pumpedthrough the laboratory plant at a mean temperature of 410° C. in thereactor. The conversion of styrene was 85.1%, and 12.5 g/h of2-methyl-4-phenyl-2-butanol were obtained in the steady state. Thesamples were analyzed by means of gas chromatography.

Step b)

A 300 ml autoclave was initially charged with 10.2 g of2-methyl-4-phenyl-2-butanol (62 mmol) from step a), dissolved in 150 mlof tetrahydrofuran, and 1.7 g of the catalyst from preparation example 1in a catalyst basket. The autoclave was purged three times withnitrogen, and then hydrogen was injected to pressure 200 bar at 200° C.for 12 hours. After 6 and 12 hours, the progress of the reaction wasanalyzed by means of gas chromatography (30 m, column material DB1,internal diameter: 0.25 mm, film thickness: 0.25 μm, temperature program50° C.-5 min isothermal; 6° C./min.→290° C.-219 min. isothermal). Theproduct contents are reported in the table which follows.

4-Cyclohexyl- 2-Methyl-4-phenyl- 4-Cyclohexyl- 2-methyl-2-butanol2-butanol 2-methylbutane  6 hours 88.9% 0% 5.9% 12 hours 88.2% 0% 6.8%

After only 6 h, no starting material was detectable any longer. The lowproportion of by-products such as 4-cyclohexyl-2-methylbutanedemonstrates the high selectivity of the hydrogenation for the desiredtarget compound 4-cyclohexyl-2-methyl-2-butanol.

Step b)

A 300 ml autoclave was initially charged with 100 g of a discharge fromstep a), which was concentrated to a 2-methyl-4-phenyl-2-butanol contentof 50%, and 5 g of the catalyst according to EP1317959 example 1B. Theautoclave was purged three times with nitrogen and then hydrogenationwas effected at 40° C. and hydrogen pressure 150 bar for 12 hours. After12 hours, the discharge was analyzed by means of gas chromatography (30m column material DB1, internal diameter: 0.25 mm, film thickness: 0.25μm, temperature program 50° C.-5 min isothermal; 6° C./min. □290° C.-219min. isothermal). The conversion of methyl-4-phenyl-2-butanol was>99.9%;

the selectivity for 4-cyclohexyl-2-methyl-2-butanol was 97.7%.

The invention claimed is:
 1. A process for preparing4-cyclohexyl-2-methyl-2-butanol, comprising: a) reaction of styrene withisopropanol at a temperature in the range from 250 500 ° C. to obtain2-methyl-4-phenyl-2-butanol, and b) heterogeneously catalyzedhydrogenation of 2-methyl-4-phenyl-2-butanol over a catalyst suitablefor ring hydrogenation of aromatics, where the molar ratio of thestyrene used in step a) to the isopropanol used in step a) is in therange from 1:below 5 to 1:0.5.
 2. The process according to claim 1,wherein the reaction in step a) is performed in the absence of acatalyst.
 3. The process according to claim 1, wherein essentially nofeedstocks other than styrene and isopropanol are used for reaction instep a).
 4. The process according to claim 1, wherein the reaction instep a) is effected under conditions under which isopropanol is in thesupercritical state.
 5. The process according to claim 1, wherein thereaction in step a) is effected at a pressure in the range from 5 to 50MPa.
 6. The process according to claim 1, wherein at least 80% of theisopropanol is initially charged and at least 80% of the styrene used instep a) is fed to the reaction in step a) under reaction conditions. 7.The process according to claim 1, wherein the reaction mixture obtainedin step a), optionally after removal of isopropanol, is fed directly tostep b).
 8. The process according to claim 1, wherein the reactionmixture obtained in step a) is subjected to a distillative purificationand the purified 2-methyl-4-phenyl-2butanol is supplied to step b). 9.The process according to claim 1, wherein the catalyst used in step b)comprises, as an active metal, palladium, platinum, iron, cobalt,nickel, rhodium iridium, ruthenium, alone or together with at least onefurther active metal of transition groups IB, VIIB or VIIIB of thePeriodic Table of the Elements (CAS version).
 10. The process accordingto claim 1, wherein the catalyst used in step b) comprises, as an activemetal, ruthenium alone or together with at least one further activemetal of transition groups IB, VIIB or VIIIB of the Periodic Table ofthe Elements (CAS version).
 11. The process according to claim 1,wherein the catalyst used in step b) is a supported catalyst whichcomprises, as an active metal, ruthenium, rhodium or nickel alone ortogether with at least one further active metal of transition groups IB,VIIB or VIIIB of the Periodic Table of the Elements (CAS version) on asupport material selected from silicon dioxide-containing, aluminumoxide-containing support materials and activated carbon supportmaterials.
 12. The process according to claim 1, wherein the catalystused in step b) is a supported catalyst which comprises, as an activemetal, ruthenium alone or together with at least one further activemetal of transition groups IB, VIIB or VIIIB of the Periodic Table ofthe Elements (CAS version) on a support material selected from silicondioxide-containing, aluminum oxide-containing support materials andactivated carbon support materials.
 13. The process according to claim12, in which the amount of the active metal is 0.1 to 1% by weight,based on the total weight of the catalyst.
 14. The process according toclaim 11, wherein the catalyst is a shell catalyst in which at least 60%by weight of the active metal is present in the shell of the catalystdown to a penetration depth of 200 μm, determined by means of SEM-EPMA(EDXS).
 15. The process according to claim 14, wherein the supportmaterial of the catalyst has a pore volume in the range from 0.6 to 1.0ml/g, determined by Hg porosimetry, and a BET surface area of 280 to 500m2/g, and at least 90% of the pores present have a diameter of 6 to 12nm.
 16. The process according to claim 1, wherein step b) is performedin trickle mode.
 17. The process according to claim 1, wherein step b)is carried out in a suspension method.
 18. The process according toclaim 1, wherein the reaction in step a ) is effected at a temperatureof 390 ° C. to 500 ° C.